Gojira tai Megaro

Inventor Goro Ibuki (Katsuhiko Sasaki) creates a humanoid robot named Jet Jaguar, which is soon seized by the undersea race of people called the Seatopians. Using Jet Jaguar as a guide, the Seatopians send Megalon as vengeance for the nuclear tests that have devastated their society. After the Seatopians' plan is botched, Jet Jaguar is completed but is taken by the Seatopian agents, who use it to guide Megalon to attack Tokyo.